The present invention relates to coating apparatuses and methods of applying coatings.
Coatings are utilized in a variety of settings to provide a variety of benefits. For example, modern gas turbine engines can include thermal barrier coatings (TBCs), environmental coatings, etc. to help promote efficient and reliable operation. Conventional electron beam physical vapor deposition (EB-PVD) and plasma-based PVD techniques used to create multilayer ceramic coatings are plagued by undesirable transition effects between layers, such as crystallographic defects that occur when coating growth is stopped and re-started and mechanical property discontinuities associated with sharp transitions from one type of ceramic to another (e.g., coefficient of thermal expansion discontinuities). These transition effects can limit a service life of the coating.
One prior art coating involved plasma spraying to deposit powdered coating material on a blade outer air seal (BOAS). According to that process, the coating material was deposited as a stream of liquid droplets. The coating was deposited on the parent material of the BOAS using continuous plasma spraying (in liquid droplet form) to form a bond coat of Nickel-Chromium/Aluminum, followed by a layer with a gradient of Cobalt-Chromium-Aluminum-Yttrium alloy and Alumina, followed by another layer with a gradient of Alumina and Yttria-stabilized Zirconia, and followed by another layer of either (a) Yttria Zirconia aromatic polyester blend or (b) Yttria-stabilized Zirconia plus Silicon or simply Yttria-stabilized Zirconia blended with an aromatic polyester material. Such a coating and an associated application method are described in U.S. Pat. Nos. 4,481,237, 4,588,607, 4,603,257 and 4,613,259.